Facile preparation of g-C₃N₄/Bi₂WO₆ hybrid photocatalyst with enhanced visible light photoreduction of Cr(VI)

A series of binary g-C₃N₄/Bi₂WO₆ hybrid photocatalysts with different ratios of g-C₃N₄ were successfully prepared using a facile hydrothermal method. The composition, structure, and optical properties of the obtained g-C₃N₄/Bi₂WO₆ composite photocatalysts were characterized by various analytical techniques including infrared spectroscopy, X-ray diffraction, UV-vis diffuse reflectance spectroscopy, N₂ adsorption-desorption measurements, X-ray photoelectron spectroscopy, and scanning electron microscopy. The photocatalytic activity of the as-prepared samples were evaluated in the reduction of toxic Cr(VI) to Cr(III) under visible light irradiation. Among all the tested catalysts, 1:15-g-C₃N₄/Bi₂WO₆ nanocomposite displays the highest photocatalytic activity with the optimal rate constant of 0.0414 min⁻¹ due to the high surface area and the improvement of visible light absorbing capacity. The composite also shows good photostability and reusability after five cyclic experiments. Different scavengers such as citric acid, oxalic acid, and isopropanol were used to systematically investigate their effect on Cr(VI) photoreduction. Appropriate concentrations of citric acid and oxalic acid have positive effect to improve the photocatalytic activity by consuming photo-induced electrons to minimize the rate of electron-hole recombination, but excessive citric acid and oxalic acid are harmful to the photoreduction. A possible mechanism for Cr(VI) photoreduction by g-C₃N₄/Bi₂WO₆ composite was proposed.